Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
A rotor speed of an alternating current (AC) machine can be measured with physical (hardware) speed sensors, such as speed encoders, tachometers, resolvers, or other position sensors. These physical speed sensors typically require additional information processing to yield information about the rotor speed of an AC machine.
As known to one of ordinary skill in the art, physical speed sensors typically suffer from a lack of reliability due to problems associated with hardware-based failures. With intent to improve reliability of AC machine drives and potentially reduce their costs, speed sensorless approaches have been shown to be valuable in applications where failures are intolerable. Applications of these speed sensorless approaches typically include electric and hybrid vehicles, ship propulsion systems, and aerospace applications.
Speed sensorless approaches may involve linear and nonlinear control and estimation theories to create speed estimators that avoid the need for physical speed sensors. These speed estimators typically involve Kalman filtering systems, model reference adaptive systems, Luenberger observer systems, and others. However, these speed estimators suffer from implementation complexity.